System of amplification of alternating current



Feb. 4, 1936.

V y L. A. GEBHARD SYSTEM OF AMPLIFICATION OF ALTERNATING CURRENT Filed July 21, 1951 Louis A. Gab/2am ATTORNEY Patented Feb. 4, 1936 sparse stares PATENT @FHQE SYSTEM OF AMP'LEFZEATION OF ALTER- NATING QUE/RENT 7 Claims.

(Granted under the act of March 3, 1883, as

amended April 30,

My invention relates broadly to a circuit arrangement for a multi-stage electron tube transmission system and more particularly to an arrangement of coupling circuit for the several stages of an electron tube transmitter for insuring the maximum transfer of energy from an oscillator circuit through a power amplification system to the transmission circuit.

This application is a continuation in part of the subject matter isclosed in application Serial No. 60,071 which I filed jointly with John M. Miller on October 2, 1925 for System for the amplification of alternating currents.

A copending application Serial No. 551,783,

which I filed jointly with John M. Miller on July 18, 1931, which has become Patent No. 1,955,341, is also a continuation in part of the subject matter of the parent application Serial No. 60,071; the latter having, in due course, become abandoned. Patent No. 1,955,341 deals more particularly with means for obtaining very high amplification ratios in successive stages of a high power transmitting system, whereas the instant case is directed to other objects such as the following: One of the objects of my invention is to provide a simplified construction of multi-stage electron tube transmission system in which a maximum amount of energy may be transferred through the several electron tube amplification stages to the transmission circuit.

Another object of my invention is to provide a circuit arrangement for a multi-stage electron tube transmission system wherein single inductance members provide the means for effecting the transfer of energy from one electron tube stage to a succeeding electron tube stage with tap connections extending to the single inductance units for balancing the operation of the amplifier system.

Still another object of my invention is to provide a circuit arrangement for the electron tube stages of a high power transmitter system in which a single coupling inductance is disposed between the output circuit of one electron tube stage and the input circuit of a succeeding electron tube stage with tap connections on the inductance leading to a tuned element for establishing a tuned path through the inductance with additional taps interconnecting the output circuit of one tube with the input circuit of the succeeding tube and providing a path for balancing the capacity coupling of the tube electrodes in the tubes constituting the several electron tube stages.

A further object of my invention is to provide an arrangement for coupling the electron tube circuits of a transmission system in which a single coupling inductance is so disposed intermediate the electron tube stages that separate 5 paths are provided through taps on the inductance for interconnecting the output of one electron tube with the input of a succeeding electron tube and establishing a tuned output circuit for the first tube while balancing the operation 10 of the electron tube stages through another path connected with the inductance.

A still further object of my invention is to provide a simplified construction of coupling circuit for the stages of a high power electron tube transmission system in which a single inductance constitutes part of the output circuit of one electron tube and the input circuit of a succeeding electron tube with tap connections thereon for balancing the circuits of the electron tube stages for insuring the maximum transfer of energy from one electron tube system to the succeeding electron tube system.

Another object of my invention is to provide a conductive coupling arrangement between a crystal controlled electron tube oscillator and a power amplifier by which maximum power may be drawn from the crystal controlled oscillator circuit and transferred to a power amplifier system having means connected with the coupling inductance for balancing the operation of the amplifier system.

Other and further objects of my invention will be understood from the specification hereinafter following by reference to the accompanying drawing which diagrammatically illustrates a crystal controlled electron tube transmitter embodying the principles of my invention.

Referring to the drawing, the electron tube I is a low power tube and generates oscillations, the frequency of which is controlled by the quartz crystal E. The crystal is shown connected between the filament and grid of the electron tubev The battery 6 supplies a negative voltage to the grid of the electron tube through the choke coil 5. The condenser 53 is a radio frequency by-pass condenser. The filament Id of the electron tube l is heated in a well-known manner with alternating current from the secondary l of a transformer having a primary winding it connected to leads H over which the alternating current is supplied. The source of continuous voltage B2 supplies the plate circuits of both the tubes I and 2 through leads 26, a reduced voltage being supplied to tube I through the voltage divider consisting of resistances 21 and 28. The plate current of tube #l is read on the ammeter I11, the plate voltage by the voltmeter E4. by-pass condenser. current is generated in the circuit comprising the parallel coil I8 and condenser 20 and is read by the ammeter I10. The connections from the condenser 20 are formed by means of taps 26a. and 2% on inductance it. The return path for the output circuit of tube l to the source of plate potential is connected through inductance l8 through tap it as shown. It will be observed that the inductance provides extremely close coupling between the portions 13 and I9 of the inductance as will be hereinafter described more in detail. The portion of the inductance shown at is is arranged in such relation to the portion of the inductance shown at!!! that balanced operation of the circuits may be obtained as explained hereinafter.

Reference character 2 designates an electron tube of much higher power rating than tube The exciting voltage is supplied to the grid of tube 2 through the connection I80. between coil l8 and the grid which includes the condenser 2| and ammeter I9. The grid is rendered negative by the voltage derived from the battery B3, through the connections 52, running from the junction of resistances 39 and M! through the sig naling key 35, the ammeter I6 and choke coil Ls to the grid 21). When the signaling key 35 is open, the grid connection is made through resistance 38 to the extreme negative terminal of the source B3 which efiectively blocks the tube so that it no longer acts as an amplifier. The negative voltage applied to the grid of the tube 2 is sufficient in actual operation, that when signaling key 35 is closed and the exciting voltage is applied, only a small grid current is registered by the ammeter I6 and only a slight reduction in the current indicated by ammeter I10 is noted. The filament 2a is supplied from the secondary E2 of a transformer having primary winding l6 connecting to supply line H. The plate supply voltage for the tube 2 is furnished by the source B2 through the leads 25, ammeter Is and choke coil 32. The condenser 22 serves as a blocking condenser for the continuous plate voltage and as a by-pass for high frequency currents.

The amplified output current of high frequency flows in the circuit comprising the coil 25, condenser 25 and ammeter I4, which circuit is connected through taps 25a and 251) with the turns of inductance shown at 25. The return plate circuit path for tube 2 extends through tap H to the balancing portion of the inductance indicated at 72.

My invention provides for a connection containing the variable condenser 23 and turns it of coil it in combination with the other features described. With a suitable number of turns IS in coil 3 and proper polarity of the tapped connection l9a, on this coil and a suitable Value of capacity in variable condenser 23, reaction is prevented between the output circuit and input circuit of the electron tube 2 through the eilec' tive capacity between the plate and grid electrodes of the tube, and other extraneous capacities such as leads, terminals and apparatus associated with the circuits. The arrangement of coil 24 with its balancing turns l2 and its associated taps is similar to the arrangement described in connection with coil 18. The turns of The condenser 3! is a high frequency The high frequency output inductance designated at I9 are closely coupled with the turns of inductance designated at E3. The tap from'the portion of inductance l8 which is taken at point l8a, on inductance [8 serves to- The tap lQa voltage in the turns l8 of the inductance is set up'for balancing the operation of the tube system through a single coupling inductance. That is to say, the current feed back through the interelement capacity of tube 2 across electrodes 21) and 20 through condenser 25 and tap its causes a voltage to be set up across turns l8 which is 180 out of phase with the voltage set up in the turns of inductance !8 due to the current through the path containing condenser 23, tap 89a and turns IS. The regulation of the balancing path is determined by moving adjustable contactor l9a or changing the effective value of variable condenser 23.

The tube 2 functions as an amplifier for iniil, serves to establish a path through which a voltage opposing the creasing the amplitude of the radio frequency energy developed by the oscillator l impressing the energy thus developed upon the electron tube mitting antenna, under normal conditions of 0peration, tube 2 might be a one kilowatt tube and tube l a five or ten watt tube. Since tube 3 is the last tube it is advantageous to excite this tube normally, thus a relatively large amount of power is taken from the exciting tube 2. Reactions between the output circuit of tube 3 and the input circuit are prevented by the connection running from the tap 63 on coil 24 and including variable condenser 52 in a similar manner to that explained before for tube 2. The supply of voltage for the plate of tube 3 is furnished by the source B4, through leads 6!, and choke coil 49. 5|, 42 and are the customary by-pass condensers. The output circuit of tube 3 includes the coupling coil 5t which is coupled to coil in the antenna system 51 and counterpoise 58. The antenna circuit is tuned by varying the position of the tap 550. on coil 55 and the variable condenser 56. Filament electrode 3a, is heated from a filament transformer comprising primary winding 46 and secondary winding 43 supplied by power through leads 51. A common. bus connection is provided for all of the tube circuits as shown. The keying circuit may be distantly controlled through winding 36 which is connected to line wire system 31.

It will be observed that the taps 20b and 25b on inductances l8 and 24 respectively, are beyond the return path taps l0 and ll on the respective inductances for increasing the balancing effect in each of the coupling systems.

I utilize a single coupling inductance disposed between the output circuit of one electron tube and the input circuit of the succeeding electron tube and utilizing the taps along the inductance units in such arrangement that the single coil functions in a multiplicity of difierent ways. When coupling the output of an oscillator to the input of the power amplifier, the coupling inductance provides an oscillatory path forthe Oscillator at the same time effecting a transfer of energy to the power amplifier and in addition effecting a balance for the operation of the electron tube circuits.

In the case of the interconnection of the output circuit of one stage of power amplification with a succeeding stage of power amplification, the single inductance provides a tuned path for the output circuit of one power amplifier stage while efiecting a transfer of energy to the input circuit of the succeeding power amplifier stage and also providing a balancing circuit for insuring the balanced operation of the several amplifier stages. This arrangement provides for the simplified assembly of an electron tube transmitter as the mechanical means for mounting the coupling inductance may be of simplified form. Better insulation may be obtained by virtue of the simplified mounting of the inductance. Greater efliciency inoperation is obtained by increase in the transfer of energy from the oscillator to the transmission circuit.

In order to eliminate the undesirable effects of the alternating current which is utilized for heating the cathodes la, 21: and 3a, a center tap is provided on the secondary windings 43, I2 and I of the filament heating transformers. In order to afford a low reactance path for the radio frequency return currents to the cathodes, condensers 8, 9, M, I5, 44 and 45 are connected across each half of the secondary windings I, I2 and 43 respectively, of the filament heating transformers. Resistances are provided in each of the voltmeter circuits. Meter E; has a resistance 30 disposed in series therewith, while meters E1, E2 and E3 have resistances 48, 4i and 29 disposed in circuit therewith. A resonance circuit including inductance 59 and ammeter I2 is disposed between the output of tube 3 and the coupling system which connect with the antenna.

Tap 10 is connected to ground through by-pass condenser 3|. Similarly tap H is connected to ground through by-pass condenser 42. These connections serve to hold the potentials of the points on the inductances to which they are connected at substantially radio frequency ground potential.

By-pass condensers 8 and 9 on the filament connections of tube I serve to hold the filament at substantially radio frequency ground potential. Similarly condensers l4 and I connected to the filament operate to hold the filament of tube 2 at substantially radio frequency ground potential. Condensers 44 and 45 serve a similar function with respect to the filament of tube 3.

The tap l8a, should be located on the same side of tap 10 as tap 23a is located. Tap 19a should be located on the other side of tap 10. This arrangement is necessary to insure the 180 phase displacement. Tap 20a may embrace the total coil and does not necessarily have to be placed at any particular arrangement with respect to tap Eta. Tap 20b may be placed as shown in the diagram or coincident with tap 10. If it is placed coincident with tap 10 then it is essential that turns I9 be coupled very closely to the turns H3 in order to obtain a satisfactory balance. This can be done by designing the coils to have a large diameter and a short length. Coils of extremely great length and small diameter have been found to be unsatisfactory. If, however, tap 20b is arranged to be coincident with tap l9a, then coupling between turns l9 and turns I8 is secured in an additional manner from that previously described, namely, through the resonant circuit comprising condenser 20, turns 18 and turns l 9. It is possible by this arrangement then to use slender coils with fairly great length.

In operation balance may be considered from two standpoints:

(a) From the standpoint that energy entering the system is not transmitted through the system and lost but is retained in the system and made to do work in the input circuit of the tube.

(1)) From the standpoint that energy in the output circuit of the tube is prevented from entering the input circuit of that same tube and causing difiiculties due to self-oscillation in that tube.

Considering the system from the first standpoint, the excitation voltage is obtained from the resonant circuit comprising coil l8 and condenser 20, from condenser 2| to the grid circuit of tube 2 comprising grid 2b and filament 2a.

The resonant circuit comprising condenser and coil 24 is therefore subject to this voltage and after this circuit is tuned to resonance will consume considerable power to such an extent that oscillations of the crystal circuit will be stopped. However with the addition of the balance, a voltage 180 out of phase with that due to the excitation voltage is impressed between the anode 2c and filament 2a through tap [9a and condenser 23. With proper adjustment of this tap and condenser it is possible to substantially utilize voltage between these terminals due to excitation and thus the reaction upon the crystal circuit of resonant circuit comprising condenser 25 and coil 24 is substantially eliminated, the energy in the crystal circuit being compelled and confined to the input circuit of tube 2.

With respect to tube 3 and its resonant input and output circuits the same method of operation is secured.

With respect to the second purpose, mainly to prevent self-oscillation in the system or regeneration injurious to the crystal in the master circuit, the system may be considered as having a voltage existing between the anode 2c and the filament 2a of tube 2. This voltage is the voltage existing in the output circuit of tube 2 which causes a current to be set up at two different paths. One of these paths is through the interelement capacity of tube 2 between its anode 2c and its grid 2b through condenser 2| and tap lBa through tap ill to ground. A second circuit com prises condenser 23, tap lilw and tap 10 to ground. The current through the first circuit causes a potential to be set up between tap 58a and tap 10 which is substantially across the input circuit of tube 2. The current through the second circuit causes a magnetic field due to passing through turns 19 which field reduces the voltage in turns [8 substantially 180 out of phase with the voltage due to the current in the first circuit. If the magnitudes of these voltages are properly adjusted the resultant voltage is zero. This may also be considered from the standpoint of coupling, in which case with this proper adjustment the coupling between the output circuit and the input circuit of the tube will be substantially zero. Thus regeneration in the tube such as might cause injury to crystal 4 or self-oscillation of the amplifier circuit is avoided.

I have found the operation of the transmission system of my invention highly practical and while I have described my invention in one of its preferred embodiments, I desire that it be understood that modifications may be made and that no limitations uponmyinvention are intended other than are imposed by the scope of the appended claims.

The invention herein described, may be manufactured and used by and for the Government of the United States of America, for governmental purposes, without the payment of any royalties thereon.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. -A radio transmitter circuit including a piezo electric crystal controlled oscillator having an input circuit and an output circuit, a power amplifier the input circuit of which is adapted to receive energy transferred from said oscillator,

means including a single inductance winding in said oscillator output circuit for coupling the same with said amplifier input circuit and for transferring energy to said amplifier, and means including a keying-circuit relay for changing the grid bias applied to said amplifier and for causing said amplifier to transmit code signals.

2. A radio transmitter circuit including an oscillator having an input circuit and an output circuit, a power amplifier'the input circuit of which is adapted to receive energy transferred from said oscillator, means including a single inductance winding in said oscillator output circuit for coupling the same with said amplifier input circuit and for transferring energy to said amplifier, and means including a keying-circuit relay for changing the grid bias applied to said amplifier and for causing said amplifier to transmit code signals.

3. In a radio transmission system, a multiplicity of electron tube stages each having input and output circuits, and means interconnecting the output circuit of one electron tube stage with the input circuit of a succeeding electron tube stage comprising a single inductance having tapped connections leading to the last mentioned circuits, a tuning element connected in shunt with a portion of said inductance, a balancing circuit connected in series with another portion of said inductance, and means including a keying-circuit relay for changing the grid bias applied to one of said tube stages and for causing said system to transmit code signals.

4. In a radio transmission system, a keyingcircuit relay, a multiplicity of electron tube stages each having input and output circuits, means for causing said keying-circuit relay to effect a change of bias potential applied to one of said input circuits, and means interconnecting the output circuit of one electron tube stage with the input circuit of a succeeding electron tube stage comprising a single inductance, said inductance having a point therein connected to ground with the turns on one side of said grounded point connected in the output circuit of one electron tube and adjustably included in the input circuit of the succeeding electron tube and the turns of said inductance on the other side of said grounded point'being connected for balancing the operation of said electron tubes.

, 5. In a radio transmission system, a multiplicity of electron tube stages each having input taps being disposed adjacent said grounded point and the other of said taps being removed from said grounded point, a tap on said inductance extending to the output circuit of one electron tube, a tap on said inductance intermediate the taps leading to said tuning condenserv for applying excitation potential to the input circuit of the succeeding electron tube, and a balancing circuit tap connected to said inductance at a point beyond the limits of the tap connecting to one side of said tuning condenser, and means including a keying-circuit relay for changing the grid bias applied to one of saidtube stages and. for causing said system to transmit code signals.

6. In a radio transmission system, a multiplicity of electron tube stages each having input and output circuits, and means interconnecting the output circuit of one electron tube stage with the input circuit of a succeeding electron tube stage comprising a single inductance, a connec- 1 electron tube, a tuning element, adjustable taps connecting said tuning element to points along said inductance displaced from said first mentioned tap, an excitation tap adjustably connected to said inductance intermediate the terminals of said tuning element and connected with the input circuit of the succeeding electron tube, a balancingtap connected to said inductance, beyond the grounded point thereof and beyond the connection of said tuning element with said inductance for establishing opposing current paths through said inductance for balancing the operation of said electron tube stages, and means including a keying-circuit relay for changing the grid bias applied to one of said tube stages and for causing said system to transmit code signals. a

7. In a radio transmission system, a multiplicity of electron tube stages each having input and output circuits and means interconnecting the output circuit of one electron tube stage with the input circuit of a succeeding electron tube stage comprising a single inductance having tapped connections leading to the last mentioned 'circuits,-a tuning condenser connected in shunt with a portion of said inductance, a balancing circuit extending from one of the circuits of the succeeding electron tube to a tap on said inductance, said tap being located beyond the connection of one side of said tuning condenser with said inductance, said balancing circuit extending through said inductance to a point intermediate the connections of said tuning condenser with said inductance for establishing paths for opposing currents through said inductance.

LOUIS A. GEBHARD. 

